Application of universal plaster is one of the stages of finishing work and performs a number of tasks. The plaster masks the external defects of the wall and evens the surface to a “finish” finish. It serves as a solid basis for subsequent finishing work, and also reduces costs, allowing you to reduce the amount of work and be limited to a minimal finish: plastering and painting. Plaster improves the waterproofing of the surface and enhances the heat and noise insulation of the wall.
Cement-sand plaster is used for such works:
- decoration of the facade of the building;
- alignment of indoor walls for further decoration (rooms with high humidity or without heating);
- concealment of screeds and cracks both on the inside and on the front side;
- elimination of significant surface flaws.
Advantages and disadvantages
The positive qualities of plaster include the following features:
- high strength;
- immunity to temperature extremes;
- excellent moisture resistance;
- good frost resistance;
- good adhesion (gluing ability) with certain types of surface: concrete, brick, stone, cinder block;
- a simple solution formula allows you to find all the necessary components in any hardware store;
- affordability, especially when preparing the solution yourself.
The negative aspects of working with cement-sand plaster include the following:
- work with the solution is physically difficult and tiring, it is difficult to even out the applied layer;
- the hardened layer is very rough, it is not suitable for direct staining or gluing of thin wallpaper without additional decoration;
- the dried surface is difficult to grind;
- increases the mass of walls and, as a result, makes the structure as a whole heavier, which is especially important for small buildings where there are no powerful load-bearing supports and a massive foundation
- poor adhesion to wood and painted surfaces;
- strong shrinkage of the layer requires a minimum of two finishing layers and cannot be applied with a layer thinner than 5 and thicker than 30 millimeters.
Composition and features
Standard solution consists of the following components:
- cement, depending on the brand of which the strength of the composition varies;
- sand - only coarse-grained (0.5-2 mm) sifted river or quarry can be used;
When mixing the solution, it is important to observe the proportions, as well as use the correct types of components. If there is too little sand, the mixture will set quickly and its strength will decrease. If you do not use sand at all, then with such a composition you can only close up minor irregularities, whereas for large-scale work it is completely unsuitable.
When using fine sand, the chance of cracking increases. The presence of impurities in the form of clay or earth reduces the strength of the hardened layer and increases the chances of cracking. If the size of grains of sand is larger than 2 mm, the surface of the hardened layer will be too rough. The sand fraction of 2.5 mm or more is used only for bricklaying and is not suitable for plastering.
Cement-sand mixture has a number of basic parameters that determine its properties.
- Density. One of the main characteristics that determines the strength and thermal conductivity of a solution. The standard composition of the plaster, without the presence of impurities and additives, has a density of about 1700 kg / m3. Such a mixture has sufficient strength for use in facade and interior works, as well as for creating floor screed.
- Thermal conductivity. The base composition has a high thermal conductivity of approximately 0.9 watts. For comparison: the gypsum mortar has three times less thermal conductivity - 0.3 watts.
- Vapor permeability. This indicator affects the ability of the finishing layer to pass the air mixture. Vapor permeability allows moisture to evaporate into the material under a layer of plaster, so that it does not become damp. Cement-sand mortar is characterized by vapor permeability from 0.11 to 0.14 mg / mPa.
- Drying speed of the mixture. The time spent on finishing depends on this parameter, which is especially true for cement-sand plaster, which gives strong shrinkage, and therefore is applied several times. At an air temperature of +15 to + 25 ° C, the complete drying of a two-millimeter layer will take from 12 to 14 hours. With increasing layer thickness, the hardening time also increases.
It is recommended to wait a day after applying the final layer and only then engage in further surface treatment.
The normal flow rate of cement-sand mortar with a standard composition with a layer of 10 millimeters is approximately 17 kg / m2. If you buy the finished mixture, this indicator is indicated on the package.
When manually creating a mortar with a mixture consumption of 17 kg / m2 with a layer of 1 cm, one should take into account a water consumption of 0.16 liters per 1 kg of dry components and a cement to sand ratio of 1: 4. Therefore, the following amount will be needed to finish 1 m2 of surface ingredients: water - 2.4 liters; cement - 2.9 kg; sand - 11.7 kg.
Work surface preparation
To ensure a reliable foundation for plastering, the wall must first be prepared. Depending on the thickness of the applied layer, type of working surface, additional reinforcing of the plaster and other conditions to obtain a qualitative result, the following actions are performed:
- Special glue is applied on the wall with a thin layer, it has excellent adhesion (adhesion to the coating material), strength and will serve as the basis for plaster. A stucco mesh is applied on top of the applied layer - so that the edges of adjacent fragments overlap with 100 millimeters. After that, with the help of a notched trowel, the mesh is leveled and pressed into the applied adhesive. The dried layer will be a strong base for cement-sand mortar.
- To further strengthen the plaster reinforced mesh is used. It is attached to the wall with self-tapping screws, creating a solid base for applying plaster with a thick layer or providing high-quality stucco coating on wooden and clay surfaces. Alternatively, wire may be used. It is wrapped between nails or self-tapping screws driven into the wall. This method is cheaper, but a large amount of manual labor is costly in time and effort. The crate is often used in small areas, where its ability to cover any area without cutting the mesh has its advantages.
- To strengthen the strength of the connection to the concrete wall, an adhesive primer is used. Before applying it to the working surface, notches and small chips are knocked out with a puncher or an ax.
- When applying new layers of plaster on top of existing ones, older ones should be checked for reliability by carefully tapping them with a hammer. The exfoliated fragments are removed, and the resulting depressions are brushed away from small pieces.
- When working with porous concrete materials before applying plaster, the surface is treated with a hydrophobic primer. This is done to reduce the absorption of moisture into the work surface from the stucco solution, which leads to its dehydration, rapid solidification and a decrease in strength.
The finished mixture is easier to use, it is advisable to buy it for small volumes of work. But if you need to cover large areas, the difference in price grows in a significant amount. In order for the solution to comply with all standards and give the desired result, you need to correctly select the proportions of the ingredients. The main indicator here is the brand of cement.
There are such options for plaster mortar:
- “200” - M300 cement is mixed with sand in a proportion of 1: 1, M400 - 1: 2, M500 - 1: 3;
- “150” - cement M300 is mixed with sand in a proportion of 1: 2.5, M400 - 1: 3, M500 - 1: 4;
- “100” - cement M300 is mixed with sand in a proportion of 1: 3.5, M400 - 1: 4.5, M500 - 1: 5.5;
- “75” - cement M 300 is mixed with sand in a ratio of 1: 4, M400 - 1: 5.5, M500 - 1: 7.
To knead a cement-sand mortar, you need to perform a number of tasks:
- Sift the sand even if it seems clean.
- If the cement is caked, its use is not recommended, but it is possible that it can also be sieved, removing lumpy inclusions. In such a mixture, the sand content is reduced by 25%.
- First, cement and sand are combined in dry form, then they are mixed until a relatively homogeneous dry mixture is achieved.
- Water is added in small portions, in between thoroughly mixing the solution.
- Further additives are added - for example, plasticizers.
An indicator of a qualitatively kneaded solution is its ability to stay in the shape of a slide without spreading. Also, it should be easily distributed over the working surface.
Wall application technique
The correct application of putty in compliance with all recommendations is one of the components of high-quality finishing work.
To do this, do the following:
- Before applying the plaster, the surface is treated with a primer - this will provide a stronger adhesion to the solution. Further the wall is allowed to dry.
- Guiding beacons are placed on the surface, by which in the process it is possible to determine the boundaries of the created plane. Their height is set according to the level; in shallow areas, they are replaced by putty flip flops. The material for the lighthouses is often a metal profile fixed to a solution of either slats or wooden bars on screws. The interval between the beacons is the length of the leveling rule minus 10-20 cm.
- To apply a standard layer (10 mm) of plaster, a trowel is used, thick - a bucket or other volumetric tool.
- A new layer is applied 1.5-2 hours after completion of the previous one. It is applied from bottom to top, completely overlapping the previous one. It is more convenient to work, breaking the wall into sections one and a half meters. Further, the plaster is stretched and aligned with the rule. This is done by tightly pressing the tool to the beacons, with a lift and a slight shift left-right. Excess plaster is removed with a trowel.
- When the solution has set, but has not yet hardened, it is time to grout. It is carried out in circular motions of the grater in places with bumps, grooves or protrusions.
- For internal work, the final hardening occurs within 4-7 days after application, subject to normal humidity. For outdoor use, this interval increases and can reach 2 weeks.
To improve the plastering work, one should delve into various subtleties, for example, machine application. To prevent cracks during quick setting, the layer is occasionally wetted with water from a spray bottle or covered with a film. There should also be no drafts, the temperature should not be elevated or fluctuate. When small cracks appear, additional grouting of problem areas is performed.
It is inconvenient to use in curved places, indentations or in the presence of various obstructing objects, for example, pipes. For such purposes, a suitable template is made, and beacons are set according to its dimensions with the necessary interval. For work with corners, a corner is used, it can be factory or manual production.
In the next video, you can clearly see how to prepare a solution for plastering walls.